Screening machine and screen cloth therefor



A, W'n'mffaELL. Y

SCREENING MACHINE AND SCREEN CLOTH THEREFOR Original Fild May 23 1919r 2 Shemts-Sheet l @y @MC June 26, E923.

B. A. MITCHELL SCREENING MACHINE AND SCREEN CLOTH THEREFOR Original Filed May 23 1919 2 Sheets-Sheet 2 Patented dune 26, ,1923.

Middag .Fihllhl FFE.

SCREENING MACHINE AND SCREEN Application led May 23, 1919, Serial To all whom it may concern.'

Be it known that I, BENJAMIN A. MITCH- nLL, a citizen of the United States, residing at St. George, Staten Island, and State of New York, have invented certain new and useul Improvements in Screening Machines and Screen Cloth Therefor, of which the following is a specification.

This invention relates to an improved form of wire screen cloth adapted for use in vibrating or stationary screens for screening ore, coal, or other materials. The invention is of particular advantage when used in screening machines wherein meansrare employed for producing tension in the screen cloth, one form of such apparatus being described and claimed in my copending application, Serial No. 258,466, filed October 16, 1918.

In vibrating screens in which the body of the screen cloth is caused to vibrate by the application thereto, by mechanical or other means, of a vibrating force applied in a plane normal to the plane of the screen, it is found that the amplitude of the vibration of the wires composing the screen cloth increases with the tension in the wires and the size and stil'ness thereof. This is due to the fact-that fine wires which have no inherent stiffness, and cannot be pulled very taut, have a tendency to muie or damp any vibration imparted to them. I-leavier wires, however, both because they may be tensioned higher and 'because they possess an inherent stiffness, are more active and resilient when set into vibration, and such cloth has a greater capacity for separating or screening the fine particles from the coarse ones.

The principal object of the present invention is to provide a which possesses the qualities ot a screen of fine mesh, while at the same time being capable of greater activity and amplitude ot vibration than other screens having a similar mesh or number of openings per square inch. rThis improvementis effected by embodying in the structure of the screen cloth Vof fine mesh and formed of fine wire, a nurnber of heavienwires which are spaced apart and extend in the direction in which tension is applied. In this construction the more active vibrations set u in the heavy wires are easily and positivelly imparted to the intervening parallel tine wires by the other wires of the woven screen which cross at right angles to the said heavy and fine wires.

form of screen clothV CLOTH THEREFOR.

No. 299,090. Renewed April 26, 1923.

Other features and advantages of the invention will appear more clearly hereinafter.7

The nature of the invention will be understood from the following specication, taken with the accompanying drawings, in which one embodiment is illustrated.

In the drawings- Figure 1 is a plan view showing the improved screen cloth mounted in a screen frame adapted to produce tension therein;

Fig. 2 shows a side elevation of the apparatus illustrated in Fig. 1;

Fig. 3 is an enlarged sectional view showing the method of connecting the screen cloth to the frame;

Fig. 4 is a side elevation of a screening machine, showing one means for producing vibrations in the tensioned screen;

Fig. 5 is a side elevation of the apparatus illustrated in Fig. 4, showing a part of the vibrator. in section;

Fig. 6 illustrates a modified formil of the invention in which an oblong mesh is formed in the screen cloth by spacing the wires running in one direction at greater intervals than the .wires running at right angles thereto; and

Fig. 7 is a plan view of another modified `form 'of the invention in which the spaced heavy wires run in .both directions.

4In the drawings the inventionis shown as comprising a woven Wire screen cloth 10, which is composed of a-series of longitudinal wires 11, and a series of transverse wires 12, each series of wires being formed of relau tively fine wire. At intervals transversely of the screen cloth heavy longitudinal wires 13 are employed in place of the line wires 11, so that a number of fine wires'a-re inter sed between and lie arallel to each palr of larger wires 13, w ich are relatively heavy .and preferably have considerable inherent stiffness.

In the practical use 'of the screen cloth, it may be mounted in a screen frame 15 having transverse flanges 16 along the opposite up-turned ends thereof, these flanges bein apertured to be engaged by bolts 17 whic are adjusted `by the nuts 18. The bolts 17 are connected at their inner ends to tubes 19, which are slotted longitudinally 0n the sides thereof opposite the bolts to receive the screen cloth 10 which is extended around rods 20 within ythe tubes. Each rod 2O is of greater diameter than thevwidth of the slot, so that when the bolts 17 are adjusted to lof lon 'tudinal strands of separate` the tubes 19, the rods l20 cause a snubbing action between the edges of the slots and the interposed portions of the screencloth, whereby a secure grip is maintained upon the screen cloth regardless of the tension produced therein by the adjustment of the bolts 17 and nuts 18. vThe heavy wires 13 of the screen cloth extend in the d1- rection in which the tension is applied, so that they operate to render the longitudinal fine wires 11 more active and to maintain a more permanent and uniform vibratory action throughout the area of the screen.

One improved method of producing vibrations in the tensioned screen is illustrated in Figs. 4 and 5, wherein the frame 15 and the screen cloth 10 carried thereby are mounted in inclined positions, so that the material to be Screened may be fed to the upper edge thereof and caused to flow down over the tensioned screen. Vibrations are produced in the screen cloth by a .rotary vibrator 25, which comprises a casing 26 having inclined rotary elements 27 therein adapted to rotate with the rotation of a shaft 28 driven by a pulley or motor 29. The casing 26 of the motor is connected to the screen cloth by plates 30 which are attached -to the ends of the casing, so that the rotary vibrations set up in the casin of the vibrator are imparted to the screen c oth in planes at right angles thereto, thereby setting up vibrations di rectly in the screen cloth, as described and claimed in my prior application above referred to.

In Fi 6 of the accompanyinor drawings, I have s own a modified form of the invention in which the screen cloth 35 is composed tine wire 36 located etween longitudinal strands 37 of heavy wire which are spaced apart and adapted to extend in the direction in which tension is applied. VThe transverse ine'wires 38 which are interwovenwith the wires 36 and 37 are arranged closer together than the longitudinal wires, so that a mesh of oblong rectangular form is produced. This construction is of advanta e since the numerous transverse wires are a apted to impart the vibrations of the longitudinal heavy wires effectively to the longitudinal fine wires.

Fig. 7 shows another modification in which the longitudinal and transverse fine wires 40 and 41 are interwoven with longitudinal and transverse heavy wires 42 and 43, respectively, the heavy wires being spaced apart. The vibrations of one set of heavy wires are effectively imparted to the fine wires through the transverse heavy wires.` l

This invention is of particular advantage when incorporated in screens of very fine mesh, for example, twenty mesh or finer. The wires in these screen cloths are very delicate, and the vibrating means must impart its vibrations thereto with great gentleness if heavy wires vgive a uniform tension imparted d irectly to the screen cloth, or, as imparted, 1n general practice in the art of very fine screening, by vibrations set up in the frame holding the screen cloth. The vibrations set up in these fine screen clothsl may be fairly active at the points of application, but in ordinary screening machines they are soon damped or smothered by the material being screened, so that a large area of the screen surface is completely deadened and not vibrating. However, with the present improvement screen cloths of line mesh can 'be operated satisfactorily and efficiently due to the fact that the heavier wires can be made heavy enough to receive a very heavy blow or vibration of large amplitude, and these being suitably spaced tend to distribute the vibrations uniformly through- 'out .the entire area of the screening surface.

It is desirable usually in screening operations to grip the edges of the screen cloth continuously, so that each wire running in vthe direction of applied tension is securely held to secure uniform tension throughout the screening-area and prevent the formation of ockets or depressions in the screening sur ace. When using the screen of the present invention, however, the heavier wires alone are positively and securely held and are subjected to a heavy tension, and while this arrangement is not adapted to throughout the entire screening area, it produces a screening surface which is free from depressions or pockets and more active and resilient when underv forced vibration than screen cloths previously known to the art.

Although I have shown particular embodiments of the invention and have explained particular applications thereof, it will be understood that the invention may be employed in various forms and uses without departing from the scope of the appended claims.

What I claim is:

1. A woven wire screen cloth adapted to be supported in a state of tension and set into vibration b impact comprising a warp and weft of re atively fine wires, said fine wires being replaced at predetermined intervals with relatively heavy wires arranged to receive initially the stress of vibration.

2. A woven wire screen cloth adapted to be supported in a state of tension from two opposite edges and set into vibration by impact comprising a warp and weft of relatively linefwires, said fine wires extendinflr ,in the direction of tension being replace vibration by impact comprising a warp and nal fine wireslongitudinally weft of relatively fine wires; the longitudibeing replaced at predetermined intervals with relatively heavy wires which are arranged' to "receive initially. the' stress of vibration.

4.' In combination, a woven screen cloth having relatively heavy wires Lextending thereof with relatively line longitudinal wires interposed therebetween, means for producing tension in said screen cloth longitudinally thereof, and means for vibrating said screen cloth.V l

5. In combination, a woven screen cloth `having relatively heavy wires extending longitudinally thereof with relatively line longitudinal wires interposed therebetween, means for prodpcing tension in said relatively heavy wires, 'and means -for producing vibrations directly in said screencloth.

6. The combination in a screening machine, of an -inclined woven wire screen clothcomprising interwoven* fine wires and heavy wires extending longitudinally of said screen cloth and interwoven with said line wires, means engaging said heavy wires for supporting said screen cloth, means for causing loose `materials over said inclined screen cloth transversely to said heavy wires, and means for impartin vibrations to said heavy wires.

The combination in a screening machine, of an inclined woven wire screen cloth comprising interwoven fine wires and heavy wires extending longitudinally of said screen cloth and interwoven with said fine wires, means engaging said heavy wires for supporting said screen cloth, means for causing loose materials to pass downwardly over said inclined screen cloth transversely to said heavy wires, and means for imparting circular vibrations to said heavy wires in planes perpendicular thereto and in alinement with the paths of travel of said materials thereover.

In testimony whereof, I have subscribed my name.

BENJAMIN A. MITCHELL.

to pass downwardly 

